Optimized geometry and limitations of compton cameras with LaBr3

LaBr₃(Ce) scintillators have a high atomic number, high light yield, and fast decay. Thus, detectors with LaBr₃(Ce) crystal can achieve high energy resolution with a significantly improved efficiency over Nal(Tl) scintillators of the same geometry. In this work, LaBr₃ was investigated for use in a Compton camera with a two-plane array design, as the material for both the scattering and absorbing detector arrays. We calculated and modeled the following properties of a LaBr₃ Compton Camera: 1) The probability of single Compton scatter; 2) Doppler broadening effects; 3) The relationships between intrinsic efficiency and angular uncertainty; 4) Optimized efficiency for a required angular resolution by selecting various geometries, such as the thickness of detectors and distance between detectors. Our study showed that Doppler broadening effects induced an intrinsic limitation of ~0.05 radian angular uncertainty for Compton cameras with LaBr₃ as the scattering detector. In comparison of LaBr₃ with other traditional scatter detector materials such as Si, we found that below thickness of ~2 cm LaBr₃ has a higher efficiency for observation of single Compton scattering events, including the hits of the recoil electron and scattered photons, than that of Si. Based on these investigations, a prototype of Compton imaging system was proposed and evaluated with Monte Carlo simulation (Geant4) also.